The present invention relates to an electron beam generator with a linear cathode which is held in clamps on at least one end and is movable in a lengthwise direction. A beam-forming electrode is associated with the cathode and is at the same potential. Connections are provided for supplying beam and heater voltage to the cathode.
Linear cathodes with movable clamping for compensating longitudinal (lengthwise) expansion are known in the art (U.S. Pat. No. 3,286,117). However, with the known electron beam generator, cathode clamping, beam-forming electrode (Wehnelt electrode) and electrical connection contacts are separate from one another with respect to design and function. This requires a special effort for the fastening of the parts and results in insulation problems, especially because of unavoidable dirt accumulation. One must keep in mind that both the cathode and the beam-forming electrode are at high negative potential up to several 10,000 Volts, that a possible second accelerator is subject to the full potential difference, and that the two ends of the cathode are additionally loaded with a heater voltage whose difference is only a few volts. Hence the known approach does not permit extremely compact design. The current supply must be rigidly clamped to the cathode ends which is possible only because the cathode is bifilar, i.e. shaped like a hairpin. However, such a cathode shape cannot be considered for the generation of sharply focussed electron beams. Furthermore, the unavoidable cathode replacement involves several operating steps and adjustments.
With so-called small guns as used especially in electron beam evaporators, it has become customary to use cathodes consisting of a wire which is bent in a more or less complicated fashion. Here, however, close tolerances must be observed, since possible position deviations of the emitting part of the cathode lead in the beam-forming electrode to a displacement of the electron trajectories and hence of the beam impact point. The results are expensive production methods and adjustments to which must be added the resistance of the cathode material to deformation.
Accordingly, it is the object of the present invention to provide an electron beam generator of the type described initially, which has an extremely compact design, is easy to manufacture, and permits the use of stretched wire sections as cathode material without subsequent adjustments.
Another object of the present invention is to provide an electron beam generator of the foregoing species which is simple in design and highly reliable in operation.
A further object of the present invention is to provide a beam generator arrangement, as described, which may be easily fabricated and economically maintained in service.